Fill up with the correct unleaded petrol for your car and avoid wasting time and money on high octane hype.

Premium unleaded petrol is more expensive than regular unleaded Petrol, but the benefits may not justify the cost. Not all cars can take advantage of the high octane in premium unleaded petrol. It pays to make an informed decision prior to arriving at the petrol pump about what petrol is best for your car and why.

Advertising on TV and radio reassures us that using special premium formulas of unleaded petrol will increase power, gain efficiency, improve mileage, protect the engine and produce cleaner emissions. Fatherly advice offered by voiceovers so deep and gravely that it could not be possible by any man with normal levels of testosterone, suggests to us that these impressive sounding premium petrol products with snazzy names and big numbers will mean greater performance of your vehicle no matter what you drive.

The average driver is unlikely to put these claims to the test. Even with a trip computer on the dashboard, it’s not all that convenient to accurately compare the performance of differently priced unleaded petrol products. So at the petrol pump we are likely to make an in-the-moment decision which often falls in favour of what we perceive to be a safer choice for our engines, the environment and on-road performance, even if it costs just a few extra dollars per pit stop.

The usual sources of impartial advice enthusiastically offered at gatherings around the water cooler, or friends and relatives at backyard BBQs on weekends, don’t help matters. Many people fill up with premium petrol brands believing that only a premium product befits their precious motor, much as they would not be seen with less than a premium beer label inserted snugly into their "World's Greatest Dad" stubby holder.

What is Premium Unleaded Petrol?
The product names of the premium petrol products will often include a number eg “Unleaded 95”. That number you see in the product name which is somewhere between 91 and 100, relates to the Research Octane Number or RON. Under the National Fuel Quality Standards Premium Unleaded Petrol (PULP) is required to have a minimum RON95, whereas regular Unleaded Petrol (ULP) has a minimum RON91. You pay more for a higher octane fuel.

In the table below you can see that petrol outlets typically offer a choice of regular unleaded petrol with RON91, premium unleaded petrol with RON95, and ultra-premium unleaded petrol with RON98.

Outlet

Product

Octane

BP

Unleaded 91

91

Premium Unleaded 95

95

Ultimate Unleaded

98

Caltex

Unleaded

91

Vortex 95

95

Vortex 98

98

Mobil

Unleaded 91

91

Premium Unleaded 95

95

Premium Unleaded 98

98

Shell

Unleaded

91

Unleaded 95

95

V-Power

98

“Octane” in petrol is not a measure of energy or power (or manhood). Research Octane Number (RON) relates to the fuels resistance to ignite under high pressure. During normal operation of the petrol engine, ignition of the fuel mix is supposed to be activated by a perfectly timed spark from the spark plug. Pre-ignition occurs when the fuel mix ignites too soon under extreme pressure within the combustion chamber. The poor timing of pre-ignition robs the engine of maximum possible power, but worse than that, the shock of the detonation could damage engine components. A knocking or pinging sound can be heard. So higher octane fuels, with a greater RON, means better resistance to pre-ignition and less chance of knocking.

High octane fuel is required to avoid engine knocking in engines operating at high ratios of compression. Not all engines operate at such extremes. Engines which are tuned for performance and operate at a high compression ratio, make use of high octane fuel to reduce the risk of knocking.

"What petrol does my car use?"
You are wasting your money if you are filling up with high octane fuel and your engine is not designed to take advantage of it. The decision about which fuel to use for best performance is not your decision to make. This has already been decided by the engine manufacturer. Assuming you have not modified your engine, and kept your car well maintained, the best fuel to use for your modern car is most likely stated on the petrol cap, or listed in the vehicles handbook.

If your car manufacturer recommends ULP, rejoice! That’s regular UnLeaded Petrol. Regular unleaded petrol is usually the cheapest unleaded petrol at the pump and provided your engine is not modified and in good shape, ULP as stated in the handbook is the best choice for your car. More expensive premium unleaded petrol with RON above 91 will not do your car any harm, but will not drastically improve performance. Save your money and treat yourself to a premium beer at your next BBQ.

If minimum RON95 or RON98 is specified for your car, you must not fill with regular unleaded. Always fill with premium unleaded petrol (PULP) at or above the minimum RON specified by your car manufacturer. The engine will be designed to take advantage of the higher octane. Using unleaded petrol with lesser octane could produce engine knocking resulting in expensive damage, especially when driven aggressively or heavily loaded.

Increasingly for some new cars, the handbook will allow a choice of either unleaded or premium petrol, but indicate that premium unleaded petrol is preferred by the car manufacture for best performance. Modern road cars fitted with advanced engine management systems can detect knocking and make adjustments so that fuel with lower octane can be used safely but with some loss of power as a downside. For these vehicles, it could be said that high octane fuel found in premium unleaded petrol will improve performance compared with using regular unleaded petrol. This is why the man with the deep voice on the ad who claims improved performance by switching to high octane premium fuel is not completely wrong. For these particular cars with the correct type of engine management system, premium unleaded petrol will improve performance. If you drive one of these cars, I’m sure the car salesman would have rammed this down your throat when you bought the car so you would already know before filling up that you have the option of filling with either premium unleaded petrol or unleaded petrol.

For older cars registered in Australia prior to 1986 which were designed to run on leaded petrol (“Super”), you may need to fill up with a high octane premium fuel, plus a lead replacement additive. Super had an octane level equal to RON97. However not all cars prior to 1986 must use premium unleaded petrol. See the AIP website for a list of older cars which can use regular unleaded petrol.

Engine Cleaning Additives

Some, but not all, premium unleaded petrol brands claim to contain additives which are said to prevent the build-up of carbon deposits, helping your engine to use fuel more economically, thus saving you money. Given the price difference between unleaded petrol and the more expensive premium unleaded petrol, I would not expect any money to be saved by filling up with premium unleaded for this reason alone.

If you like the idea of a fuel that cleans your engine, consider a petrol brand such as Shell which has the same cleaning additives across all their unleaded petrol products. For example if I fill up with Shell regular Unleaded petrol, I know I am getting the same engine cleaning formula as the more expensive premium Unleaded95 petrol product.

Anti Friction Additives

Special anti-friction lubricants are often reserved for the very top end of the premium unleaded petrol range, intended for high performance engines. For example according to Shell literature, the addition of what Shell call “Friction Modification Technology” is attributed only to the most expensive Shell V-Power product, which has an octane level far exceeding the needs of an average vehicle. Marketing petrol products in this way makes us feel as if we are missing out on something unless we buy the most expensive product. If your car engine is tuned for high performance and you drive to its very limits, then the anti friction additives are a handy feature of ultra premium unleaded petrol.

Ethanol in Petrol

Just when we've finally sorted out what unleaded petrol is best for your car, along comes bio-fuels to make the decision at the pump even more confusing. The comparison and advantages of E10 vs Unleaded is now covered in a new post.

My SAAB 93 Turbo is a perfect example of what you say. It's tuned for 95 RON but the ECU can dumb itself down to handle 91 RON without any knocking if required. However, SAAB themselves say it can't take advantage of using 98 RON so there's no point in using anything other than 95 RON for best performance and mileage.

Ironic that if you drove a throbbing Aussie V8 running on regular unleaded you may well have worse fuel economy than the SAAB, but bottom line is more cash in your pocket at the end of the day and just as much fun on the road in my personal opinion. You gotta love Australian irony.

hi foo. i have a 1976 RAMBLER 360 V8 which in the day was designed to run on 'super' fuel.as it has been rebuilt and only run a few hours what fuel would give me performance and cost efficiency.currently i have been using unleaded with an additive,but that is a nuisance having to put in each tank fill.the vehicle is not a daily driver,weekend shows/cruises only.your advice please.

You make an excellent point that I didn't mention which is the need for a lead replacement additive with older cars. I have now updated the post. Your 1976 Rambler is not likely to be listed on the AIP website for Australian cars and manufacturer imports. Try an equivalent local fuel authority or the car manufacturer or special interest group for advice. For now, stick with the additive routine unless better information arises and consider it a labour of love for the dear old thing. On the up side you'll never have to worry about value depreciation on a car like that which is the single biggest cost of owning a new car.

I have a 2007 SAAB 9-3 Linear Sport which I have been running on United E10 lately and it's worse than using 91 RON. However, today I filled up with P100 and it's like I've got an extra two cylinders. It's go so much more power and it's so much smoother. How can this be so, Grasshopper?!

It's actually cheaper to get 95 Octane by mixing 91 and 98 (Premium), rather than getting 95 directly from the pump. Most pumps will allow you to take 2 shots of fuel with the same transaction. I've been using 20 litres 98 plus 30 litres 91 in my Mazda 6 for years. -That's about 94 octane, and it's a few cents cheaper than 95. Usually, 95 price is inflated for what you get.

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NOTE: All prices on this website are shown in AUD$. Prices will change and businesses may close without notice. Amounts shown here should be used as indications only.Advice is of a general nature. Apply recommendations to your specific problems at your own risk.